How can a nation today get another nation to do something without theatening war?

Trading something they want for it. (In terms of goods AND services)

Explanation:

Say we want China to see us bamboo. We ask China if they will and they say no, but we have a certain kind of flower that China likes to use in their tea. We say, "hey, I will give you 30 trees for 30 bamboo plants."

can you explain it better

answer; the president uses mass media to gain support for policies;